Gasoline engines use a pressurized fuel system wherein a computer is used to vary the actuation of the fuel injectors to meet a demand based on the input from various sensors. Since gasoline engines have an ignition system to ignite an air/fuel mixture in the cylinders, the fuel pressure only needs to be high enough to provide an adequate spray pattern to ensure efficient combustion. Diesel engines, on the other hand, use heat from compression to ignite the air/fuel mixture. The high compression levels require correspondingly high air/fuel mixture injection pressures, as well as appropriate control and delivery systems.
FIG. 1 shows one variant of a typical HEUI fuel system 10 adapted for an 8-cylinder direct-injection diesel-cycle internal combustion engine, disclosed in U.S. Pat. No. 5,757,259 issued to Fulford et al. on May 26, 1998, hereby incorporated by reference. As shown therein, HEUI fuel system 10 includes one or more hydraulically-actuated electronically-controlled injectors 18 positioned in a respective injector bore, an actuating fluid supplying means 20 for supplying hydraulically-actuating fluid to each injector 18, apparatus or fuel supplying means 22 for supplying fuel to each injector 18, and apparatus or electronically-controlling means 24 for electronically controlling the fuel injection quantity, injection timing, and/or fuel injection pressure of the injectors 18 independent of engine speed and load.
Another example of a HEUI fuel system may be found, for example, in U.S. Pat. No. 5,191,867 issued to Glassey et al. on Mar. 9, 1993.
The hydraulically actuating fluid supplying means 20 includes an actuating fluid sump 26 (e.g., an engine lubrication oil sump, crankcase, or oil pan), a relatively low pressure actuating fluid transfer pump 28, an actuating fluid cooler 30, one or more actuating fluid filters 32, a source or actuating fluid pressurizing means 34 for selectively pressurizing actuating fluid to a variable relatively higher pressure than that delivered to it by the transfer pump 28, at least one relatively high pressure actuating fluid manifold 36,38, and an actuating fluid pressure controlling means 40 for electronically or variably controlling the magnitude of the actuating fluid pressure supplied to the injectors 18 via the manifold(s) 36,38. The hydraulic supply pump is a seven piston fixed displacement axial piston pump. During normal engine operation, pump output pressure is controlled by a Rail Pressure Control Valve (RPCV) 58, an electrically operated dump valve which closely controls pump output pressure by dumping excess flow to a return or drain circuit. A variable signal current from an electronic control module (ECM) 160 to the RPCV 58 determines pump output pressure, which is generally maintained between 400 psi and 3000 psi during normal engine operation.
One actuating fluid manifold 36,38 is provided for and associated with each cylinder head having a bank of injectors 18. Each manifold 36,38 accumulates pressurized actuating fluid delivered by the pressurizing means 34 and intermittently feeds such pressurized actuating fluid to an actuating fluid inlet passage of each hydraulically-actuated fuel injector 18 associated with that manifold. Each actuating fluid manifold 36,38 has one common rail passage 42,44 and a plurality of individual rail branch passages (not shown). Each common rail passage 42,44 is arranged downstream of the pressurizing means 34 and is in fluid communication between the pressurizing means 34 and the respective bank of injectors 18. The number of rail branch passages for each manifold 36,38 corresponds to the number of injectors 18 positioned in each cylinder head. Each rail branch passage extends between its respective common rail passage 42,44 and an actuating fluid inlet passage of a respective injector 18.
The means 24 for controlling the actual fuel injection quantity, injection timing, and/or fuel injection pressure of the injectors 18 includes the aforementioned ECM 160 and an electronic drive unit (EDU) 162. ECM 160 includes software and hardware that cooperatively define optimum fuel system operational parameters and controls both the RPCVs 58 and the injectors 18 through appropriate sensors and control circuitry and devices. For example, sensor 56 is electrically connected to the ECM 160 and provides signals indicative of the magnitude of the actuating fluid pressure in the manifolds 36,38. ECM 160 is also electrically connected to EDU 162, which in turn is connected to the solenoid or other electrically-controllable actuator of each injector 18. EDU 162 is thus configured to energize an injector 18 solenoid (not shown) so as to lift the injector 18 poppet valve (not shown) off its seat and permit fuel discharge, the fuel being supplied to injector 18 by a line connected to fuel tank 22, from injector 18. Fuel injection stops when the ECM 160 signals the EDU 162 to stop the current to the solenoid, whereupon termination of the current permits an injector poppet spring (not shown) to close the poppet valve and block the high pressure supply oil from the rail from discharge through the injector 18.
Pressurizing means 34 includes an actuating fluid pump 48, such as a gear-driven fixed-displacement axial piston pump 48. As indicated by dashed lines in FIG. 1, the actuating fluid pump 48 includes a first passage 50 adapted to be in fluid communication with the relatively high pressure pumping chamber(s) of the pump 48 and a second passage 52 or manifold pressure chamber adapted to be in continuous fluid communication with each of the manifolds 36,38. A third passage 54 is adapted to be in continuous fluid communication with the relatively low pressure actuating fluid sump 26.
As shown in FIG. 1, the actuating fluid pressure controlling means 40 includes at least one actuating fluid pressure sensor or transducer 56 and a proportional pressure control valve assembly 58 to control rail pressure. Sensor 56 is positioned on a manifold 36,38 downstream of pump 48 but upstream of injectors 18 in the actuating fluid flowpath. Valve 58 is typically adapted to be installed in the backplate of pump 48 and is configured to selectively bypass a variable amount of actuating fluid from the relatively high pressure pump 48 back to the relatively low pressure sump 26 via passage 54.
As shown in FIG. 2, also disclosed in the aforementioned U.S. Pat. No. 5,757,259 issued to Fulford et al., rail pressure control valve (RPCV) 58 includes an adapter 62 having an adapter bore 64, a cylindrical tube 66 connected to the adaptor 62, a tube stop 68 connected to or formed on one end portion of the tube 66, an axially-movable armature 76, a stator or pole piece 78 connected to adapter 62 via an internal wall defining adapter bore 64, an axially-movable push pin 80, an axially-movable pilot poppet 82, a cage 84 connected to the internal wall defining adapter bore 64, a poppet seat member 86 positioned between adapter 62 cage 84, an axially-movable (valve) spool 88, a first helical compression spring 90, a pilot stage edge filter cartridge 92, and a second helical compression spring 94.
Stator 78 and movable armature 76 collectively define an expandable armature chamber 96. Stator 78 and poppet seat 86 collectively define a pilot pressure chamber 97. Poppet seat 86, one end portion of the spool 88, and cage 84 collectively define a set pressure chamber 98. Cage 84 and another end portion of the spool 88 collectively define a valve inlet pressure chamber 100. A counterbore of the pump 48 and the cage 84 collectively define a drain chamber 104 arranged in continuous fluid communication with the sump 26 via the third internal passage 54. Stator 78 includes a vent passage 112, such as a slot extending across the outer surface of the stator 78, arranged in continuous fluid communication between armature chamber 96 and the pilot pressure chamber 97.
Poppet seat member 86 includes a bore slidably receiving poppet 82, a frusto-conical seat positioned at an end portion of the bore wherein the seat is selectively opened or closed by the movable poppet 82, one or more radial passages 118 positioned downstream of the seat and in continuous fluid communication with the pilot pressure chamber 97. An orifice 122 is adjacent to an upstream of the seat and a restricted passage 120 downstream of the orifice 122 are arranged in continuous fluid communication with the set pressure chamber 98. The movable poppet 82 selectively closes and opens fluid communication between set pressure chamber 98 and the pilot pressure chamber 97 depending upon whether the seat is closed or opened by poppet 82.
Adapter 62 includes a restricted pilot drain passage 124 arranged in continuous fluid communication with the sump 26 via the drain chamber 104 and the passage 54. Passage 124 includes a pilot drain orifice 126, extending radially outwardly from the adapter bore 64 to the outer periphery of the adapter 62, and a peripheral drain slot 128 intersecting the orifice 126. Restricted pilot drain passage 124 helps isolate and stabilize the fluid pressure in the pilot pressure chamber 97 from the relatively-lower-pressure drain passages leading to the sump 26. The restricted passage 124 also helps to maintain the pressure in the armature chamber 96 and pilot pressure chamber 97 at a predetermined level (e.g., slightly pressurized) to prevent air entrained in the actuating fluid from coming out of solution at least until the actuating fluid exits the RPCV 58. The restricted passage 124 also creates a hydraulic lock in chambers 96,97 so as to restrict or inhibit actuating fluid from draining from the chambers 96,97 after the HEUI fuel system 10 is shutoff. The restricted passage 124 effectively also lowers the pressure gain across the restricted passage 120 of the poppet seat 86 by maintaining a minimum pressure level in the armature chamber 96.
Cage 84 includes one or more radially-extending drain passages 130. Spool 88 has a reduced diameter end portion or annulus 132 facing the valve inlet pressure chamber 100 which selectively registers with the drain passages 130 of the cage 84.
The hydraulic energy of the pressurized oil permits injection of the fuel/air mixture into the combustion chamber by the injector 18. The pressure of the incoming oil controls the speed of the injector's intensifier piston (not shown) and plunger (not shown) movement, and therefore, the rate of injection. The amount of fuel injected is determined by the duration of the pulse from the EDU and energization of the solenoid.
When the engine is off, as shown in FIG. 2, spool 88 is held to the right by return spring 90 and the drain passages 130 are closed, isolating the system from sump 28. A predetermined starting actuating fluid pressure is required to start the engine. To start even a relatively warm engine, approximately 1,500 psi of oil pressure is generally required. If the engine is cold (i.e., coolant temperature is below 32° F.), approximately 3000 psi of oil pressure is generally required for start. During cranking, the ECM 160 sends a signal to the RPCV 58 to provide a minimum predetermined actuating fluid pressure to manifolds 36, 38.
During start-up or cranking, pump outlet pressure enters the right-end of the body through manifolds 36, 38, as illustrated, and a small amount of oil flows into the spool chamber or set pressure chamber 98 through the pilot stage filter screen 92 and control orifice 166 provided in the spool 88. At this time, the ECM 160 provides a signal causing the solenoid to generate a magnetic field proportional to the current applied to the solenoid coils 142 which biases the armature 76 to the right, toward the stator 78. The armature 76 exerts a force on the push pin 80 and poppet 82 to seat the poppet 82 against the seat of the poppet seat member 86. This closes passage 120 and permits fluid pressure to increase in the spool chamber 98. Thus, the combination of spool spring 94 force and spool chamber 98 pressure holds the spool 88 to the right so as to close drain ports 130. All oil provided by the pump is accordingly directed to the pressure rail manifolds 36, 38 until the desired minimum starting fluid pressure is reached.
Once the desired minimum starting fluid pressure for starting is reached, the ECM 160 sends a signal to the RPCV 58 to modulate so as to provide an actuating fluid pressure in the manifolds 36, 38 commensurate with operating conditions. This control loop is achieved by ECM 160 measurement of actual manifold pressure by means of a pressure sensor 56 and appropriate adjustment of the signal (i.e., electrical current) applied to the RPCV 58 to provide measured bleed from the spool chamber 98 through drain passages 130 to sump 26.
During normal engine operation, pump outlet pressure enters the (right) end of the RPCV 58 body and a small amount of oil flows into spool chamber 98 through the pilot stage filter 92 and control orifice 166, as noted above. The pressure in spool chamber 98 is controlled by adjusting the position of poppet 82, which permits bleed off of oil from the spool chamber 98 through drain passages 130. The position of poppet 82 is controlled by the strength of the magnetic field of the solenoid coils 142, which depends upon the current supplied by ECM 160. The spool 88 responds to pressure changes in the spool chamber 98 on the left side of the spool by axial translation to maintain a force balance between the right and left side of the spool. The axial position of spool 88 determines how much area of the drain passage 130 ports are open to spool chamber 98 and this open area directly affects the quantity of oil bled off and, correspondingly, rail or manifold 36, 38 pressure. In operation, the ECM 160 and RPCV 58 are highly responsive; and the spool 88 rapidly responds to pressure changes on either side of the spool by axial-translation about a partially-open position.
Ideally, as shown in FIG. 3, there is an ideal pressure output by the RPCV 58 in accord with a specified current supplied to coils 142 by ECM 160. For example, a current of 0.8A should produce an output pressure of about 4000 psi. However, current RPCV's and related valves are limited in both valve-to-valve variability and accuracy. The valve-to-valve variability for such valves has been known to approach ±25% of the ideal curve. In view of the ever increasing sophistication of automobile engine control systems and omnipresent need for improved fuel efficiency, improved power, and decreased emissions, such valve-to-valve variability and accuracy limitations are potentially insufficient to meet the needs of future engine designs. Further, such variability undesirably increases manufacturing costs.
Therefore, it is desirable to provide a method and device for reducing variability between electromagnetically actuated devices and improving accuracy of such devices and products incorporating such devices. As one example, for such pressure regulating valve applications as discussed above, it is desirable to reduce valve-to-valve variability and improve accuracy.